Lecture 3 



— 59 — 



Absorption 



absence of other limiting factors. The temperature 

 acceleration of salt accumulation is not necessarily of 

 the same magnitude for all ions and thus the degree 

 of selective absorption of ions may be different at 

 different temperatures. With respect to the nitrate 

 ion consideration must also be given to the influence 

 of temperature on the reduction of nitrate in the root 

 tissues after nitrate ions have been absorbed. 





Textfigure 12. — Effects of bubbling air and Nj gas 

 through the external solution on CO2 production by ex- 

 cised barley roots. A large amount of CO: is evolved 

 anaerobically, but this does not result in salt accumula- 

 tion. (From HoAGLAND and Broyer, 1942). 



Carbohydrate must be available for the respiratory 

 or other metabolic processes associated with salt ac- 

 cumulation. Direct evidence of this requirement was 

 furnished by experiments in which the sugar content 

 of the roots was reduced to a low value by aerating 



